Liquid Crystal Display Device and Manufacturing Method Thereof

ABSTRACT

A liquid crystal display device includes a first insulation substrate and a second insulation substrate which hold a liquid crystal material therebetween, a pixel electrode, a common electrode, a thin film transistor which has a semiconductor layer, a first electrode connected with a video signal line, and a second electrode connected with the pixel electrode. The semiconductor layer overlaps and is in physical contact with the pixel electrode, and a part of the pixel electrode, a part of the semiconductor layer, and a part of the second electrode are stacked at an overlapping portion.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. application Ser. No.13/296,264, filed Nov. 15, 2011, the contents of which are incorporatedherein by reference.

The present application claims priority from Japanese applicationJP2010-257428 filed on Nov. 18, 2010, the content of which is herebyincorporated by reference into this application.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a liquid crystal display device and amanufacturing method thereof.

2. Description of the Related Art

Conventionally, as a liquid crystal display device used in a televisionreceiver set or the like, there has been known a liquid crystal displaydevice where a switching element such as a thin film transistor isprovided for each pixel, and driving of a desired pixel is controlled bya switching operation of the switching element. Such a liquid crystaldisplay device includes a liquid crystal display panel where a liquidcrystal material is held between a TFT substrate on which thin filmtransistors are formed and a counter substrate on which color filtersare formed.

With respect to the TFT substrate and the counter substrate, usually, 6to 8 sheets of photo masks are used for manufacturing the TFT substrate.Exposure treatment using these photo masks and development, film peelingand etching treatment relating to the exposure treatment are factorswhich increase a manufacturing cost. That is, when a large number ofphoto masks are used, a manufacturing cost of a liquid crystal displaydevice is pushed up. Accordingly, to reduce the manufacturing cost,there has been a demand for a liquid crystal display device and amanufacturing method thereof which can reduce the number of photo masksused in the manufacture of the liquid crystal display device to 5 or 4sheets.

With respect to a liquid crystal display device, there has been known aliquid crystal display device having the constitution where sourceelectrodes, pixel electrodes and semiconductor layers are present on thesame layer, and the source electrodes and the pixel electrodes aredirectly connected with each other in a conductive manner not viacontact holes.

In the liquid crystal display device having such a constitution, amongdefects which occur in the manufacturing steps, the number ofdisconnection defects of video signal lines is large. That is, theliquid crystal display device has a drawback that the disconnectiondefects of the video signal lines lower a yield in the manufacture ofthe liquid crystal display device.

As a cause of such disconnection defects of the video signal lines,considered is a case where when the pixel electrodes are formed afterforming the video signal lines, due to the impregnation of an etchantused at the time of forming the pixel electrodes, the video signal linesare dissolved. To overcome the above-mentioned drawback, there has beenproposed a liquid crystal display device and a manufacturing methodthereof which can reduce the number of photo masks and also can reducedisconnection defects of video signal lines (see JP 2005-157016 A, forexample).

In the liquid crystal display device and the manufacturing methodthereof described in JP 2005-157016 A, the number of photo masks isreduced by performing collective etching treatment which uses a halfexposure technique, and the number of disconnection defects of videosignal lines is reduced by forming video signal lines after formingpixel electrodes.

However, in the liquid crystal display device and the manufacturingmethod thereof described in JP 2005-157016 A, scanning signal lines areformed after forming semiconductor layers and hence, the semiconductorlayer is formed with a width equal to or slightly narrower than a widthof a gate electrode whereby the requirement on accuracy of maskalignment at the time of forming a source-drain line formed on thesemiconductor layer becomes strict thus causing a drawback that aprocess design becomes difficult eventually.

It may be possible to cope with such a drawback by reducing a filmthickness of a resist pattern using oxygen plasma treatment withstrengthened anisotropy or by making a design in which a size changeamount of the resist pattern is taken into account. However, thedifficulty in process design remains even in such a case.

SUMMARY OF THE INVENTION

The present invention has been made under the above-mentionedcircumstances, and it is an object of the present invention to provide aliquid crystal display device and a manufacturing method thereof whichcan enhance a yield while reducing a manufacturing cost, and can providea process design easily.

To overcome the above-mentioned drawbacks and to achieve theabove-mentioned object, according to one aspect of the presentinvention, there is provided a liquid crystal display device whichincludes: a first insulation substrate and a second insulation substratewhich hold a liquid crystal material therebetween; scanning signal linesformed over a surface of the first insulation substrate on aliquid-crystal-material side; a first insulation layer which is formedover the scanning signal lines and on the surface of the firstinsulation substrate on the liquid-crystal-material side; semiconductorlayers and pixel electrodes which are formed over the surface of thefirst insulation layer on the liquid-crystal-material side; and a secondinsulation layer which is formed between the pixel electrodes and acommon electrode, wherein the liquid crystal display device furtherincludes: source electrodes each of which includes an overlappingportion which is a stacked portion constituted of the semiconductorlayer and a metal layer formed over a surface of the semiconductor layeron the liquid-crystal-material side and is a portion overlapping asurface of the pixel electrode on the liquid-crystal-material side;video signal lines each of which is formed of a stacked portionconstituted of the metal layer and the semiconductor layer; and drainelectrodes each of which is formed of a stacked portion constituted ofthe metal layer and the semiconductor layer, and opening portions eachof which exposes a joining portion which is a portion leading to asurface of the pixel electrode on the liquid crystal material side froma surface of the source electrode on the liquid crystal material sidevia an edge portion of the overlapping portion are formed in the secondinsulation layer, and a conductive film which is formed into the commonelectrode is formed over the joining portion exposed by the openingportion.

In the liquid crystal display device having the above-mentionedconstitution, the conductive film covers the whole surface of theopening portion.

To overcome the above-mentioned drawbacks and to achieve theabove-mentioned object, according to another aspect of the presentinvention, there is provided a method of manufacturing a liquid crystaldisplay device which includes: a first insulation substrate and a secondinsulation substrate which hold a liquid crystal material therebetween;scanning signal lines formed over a surface of the first insulationsubstrate on a liquid-crystal-material side; a first insulation layerwhich is formed over the scanning signal lines and on the surface of thefirst insulation substrate on the liquid-crystal-material side;semiconductor layers and pixel electrodes which are formed over thesurface of the first insulation layer on the liquid-crystal-materialside; and a second insulation layer which is formed between the pixelelectrodes and a common electrode, the method including a collectivelyforming step in which, after the pixel electrodes are formed over thesurface of the first insulation layer on the liquid crystal materialside, by collectively applying etching treatment to the semiconductorlayer and a metal layer, source electrodes each of which includes anoverlapping portion which is a stacked portion constituted of thesemiconductor layer and the metal layer formed over a surface of thesemiconductor layer on the liquid-crystal-material side and is a portionoverlapping a surface of the pixel electrode on theliquid-crystal-material side, video signal lines each of which is formedof a stacked portion constituted of the metal layer and thesemiconductor layer, and drain electrodes each of which is formed of astacked portion constituted of the metal layer and the semiconductorlayer are formed; an opening forming step in which opening portions eachof which exposes a joining portion which is a portion leading to asurface of the pixel electrode on the liquid crystal material side froma surface of the source electrode on the liquid crystal material sidevia an edge portion of the overlapping portion are formed in the secondinsulation layer; and a conductive film forming step in which aconductive film which is formed into the common electrode is formed overthe joining portion exposed by the opening portion.

In the method of manufacturing a liquid crystal display device havingthe above-mentioned constitution, the conductive film which is formed inthe step of forming the conductive film covers the whole surface of theopening portion.

Also in the method of manufacturing a liquid crystal display devicehaving the above-mentioned constitution, the step of forming the openingportion is performed along with the formation of openings in the secondinsulation layer other than the opening portions.

In the liquid crystal display device of the present invention, thesource electrodes each of which includes the overlapping portion whichis the stacked portion constituted of the semiconductor layer and themetal layer formed over the surface of the semiconductor layer on theliquid-crystal-material side and is the portion overlapping the surfaceof the pixel electrode on the liquid-crystal-material side; the videosignal lines each of which is formed of the stacked portion constitutedof the metal layer and the semiconductor layer; and the drain electrodeseach of which is formed of the stacked portion constituted of the metallayer and the semiconductor layer are formed, and the opening portionseach of which exposes the joining portion which is the portion leadingto the surface of the pixel electrode on the liquid crystal materialside from the surface of the source electrode on the liquid crystalmaterial side via the edge portion of the overlapping portion are formedin the second insulation layer, and the conductive film which is formedinto the common electrode is formed over the joining portion exposed bythe opening portion.

Due to such a constitution, after forming the pixel electrodes, thevideo signal lines, the semiconductor layers, the drain electrodes andthe source electrodes can be formed by collective etching treatment.

Further, the semiconductor layers can be formed after the formation ofthe scanning signal lines, the accuracy in mask alignment can be easilyacquired compared to a case where the scanning signal lines are formedafter forming the semiconductor layers.

Accordingly, the liquid crystal display device according to the presentinvention can enhance a yield while reducing a manufacturing cost, andcan provide a process design easily.

The method of manufacturing a liquid crystal display device according tothe present invention includes: the collective forming step in which,after the pixel electrodes are formed over the surface of the firstinsulation layer on the liquid crystal material side, by collectivelyapplying etching treatment to the semiconductor layer and the metallayer, the source electrodes each of which includes the overlappingportion which is the stacked portion constituted of the semiconductorlayer and the metal layer formed over the surface of the semiconductorlayer on the liquid-crystal-material side and is a portion overlappingthe surface of the pixel electrode on the liquid-crystal-material side,the video signal lines each of which is formed of the stacked portionconstituted of the metal layer and the semiconductor layer, and thedrain electrodes each of which is formed of the stacked portionconstituted of the metal layer and the semiconductor layer are formed;the opening portion forming step in which the opening portions each ofwhich exposes the joining portion which is the position leading to thesurface of the pixel electrode on the liquid crystal material side fromthe surface of the source electrode on the liquid crystal material sidevia the edge portion of the overlapping portion are formed in the secondinsulation layer; and the conductive film forming step in which theconductive film which is formed into the common electrode is formed overthe joining portion exposed by the opening portion.

Due to such a constitution, after forming the pixel electrodes, thevideo signal lines, the semiconductor layers, the drain electrodes andthe source electrodes can be formed by collective etching treatment.

Further, the semiconductor layers can be formed after the formation ofthe scanning signal lines and hence, the accuracy in mask alignment canbe easily acquired compared to a case where the scanning signal linesare formed after forming the semiconductor layers.

Accordingly, the method of manufacturing the liquid crystal displaydevice according to the present invention can enhance a yield whilereducing a manufacturing cost, and can provide a process design easily.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view showing the constitution of a liquid crystaldisplay device according to an embodiment of the present invention;

FIG. 2 is an equivalent circuit diagram for explaining the constitutionof the pixel of a liquid crystal display panel shown in FIG. 1;

FIG. 3 is a cross-sectional view of an essential part of the liquidcrystal display panel shown in FIG. 1;

FIG. 4A is a view showing a manufacturing step of a TFT substrate shownin FIG. 3, and FIG. 4B is a cross-sectional view of the structure shownin FIG. 4A taken along a line 4B-4B;

FIG. 5A is a view showing a manufacturing step of the TFT substrateshown in FIG. 3, and FIG. 5B is a cross-sectional view of the structureshown in FIG. 5A taken along a line 5B-5B;

FIG. 6A is a view showing a manufacturing step of the TFT substrateshown in FIG. 3, and FIG. 6B is a cross-sectional view of the structureshown in FIG. 6A taken along a line 6B-6B;

FIG. 7A is a view showing a manufacturing step of the TFT substrateshown in FIG. 3, and FIG. 7B is a cross-sectional view of the structureshown in FIG. 7A taken along a line 7B-7B;

FIG. 8A is a view showing a manufacturing step of the TFT substrateshown in FIG. 3, and FIG. 8B is a cross-sectional view of the structureshown in FIG. 8A taken along a line 8B-8B; and

FIG. 9 is a view showing a liquid crystal display device according to amodification of the embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Hereinafter, a preferred embodiment of a liquid crystal display deviceand a manufacturing method thereof according to the present inventionare explained in detail in conjunction with drawings.

Embodiment

FIG. 1 is a schematic view showing the constitution of a liquid crystaldisplay device 1 according to an embodiment of the present invention.

The liquid crystal display device 1 includes a liquid crystal displaypanel 10, video signal lines DL, scanning signal lines GL, a data drivecircuit 11, a scanning drive circuit 12, a backlight not shown in thedrawing and a control part not shown in the drawing.

The liquid crystal display panel 10 includes the plural video signallines DL (DL₁, . . . , DLi, . . . , DLn: i and n being natural numbers)which extend in the Y direction in the drawing, and the plural scanningsignal lines GL (GL₁, . . . , GLj, . . . , GLm: j and m being naturalnumbers) which extend in the X direction in the drawing. A displayregion AR is formed in a region of the liquid crystal display panel 10including a center portion.

The data drive circuit 11 is provided for generating a video signal(gradation voltage) inputted to the plural video signal lines DLrespectively.

The scanning drive circuit 12 is provided for sequentially inputting ascanning signal to the plural scanning signal lines GL. The data drivecircuit 11 and the scanning drive circuit 12 are electrically connectedto the liquid crystal display panel 10 via a flexible printed circuitboard or the like not shown in the drawing which is connected to anouter peripheral portion of the liquid crystal display panel 10.

The backlight not shown in the drawing is realized by light emittingdiodes or the like, and is provided for irradiating light to the liquidcrystal display panel 10 from a back surface side of the liquid crystaldisplay panel 10

The control part not shown in the drawing is realized by a CPU or thelike, and the control part is electrically connected to respective partsof the liquid crystal display device 1 including the data drive circuit11, the scanning drive circuit 12 and the backlight not shown in thedrawing so as to control an operation of the whole liquid crystaldisplay device 1.

Next, the constitution of pixels of the liquid crystal display panel 10is explained. FIG. 2 is an equivalent circuit diagram for explaining theconstitution of the pixel PIX of the liquid crystal display panel 10shown in FIG. 1.

In the liquid crystal display panel 10, as shown in FIG. 2, a regionsurrounded by a pair of neighboring scanning signal lines GL and a pairof neighboring video signal lines DL forms the pixel PIX. Each pixel PIXis provided with a thin film transistor TFT. Each pixel PIX includes apixel electrode MIT, a common electrode CT (CT₁, . . . , CTj, . . . ,CTm: j and m being natural numbers), a capacitance element Cst which isa storage capacitance formed by an insulation layer sandwiched betweenthese electrodes, and a capacitance element Clc formed by a liquidcrystal layer.

The liquid crystal display panel 10 is explained in detail using FIG. 3.FIG. 3 is a cross-sectional view of an essential part of the liquidcrystal display panel 10 shown in FIG. 1.

In the liquid crystal display panel 10, as shown in FIG. 3, a liquidcrystal material 40 is sealed between a TFT substrate 20 and a countersubstrate 30. In the TFT substrate 20, the scanning signal lines GL areformed on a surface of an insulation substrate SUB1 formed of a glasssubstrate or the like on a liquid-crystal-material-40 side. The scanningsignal lines GL are formed by applying etching treatment to a conductivefilm made of aluminum or the like using a photolithography method, forexample.

A first insulation layer PAS1 which constitutes a gate insulation layeris formed over the scanning signal lines GL. The first insulation layerPAS1 is a layer formed of a silicon nitride (SiN) film.

On the first insulation layer PAS1, semiconductor layers ASI each ofwhich is a layer constituted of the pixel electrode MIT and an amorphoussilicon (a-Si) film are formed.

Over the semiconductor layer ASI, the video signal line DL (drainelectrode SD1) which is formed of a stacked portion constituted of ametal layer M and the semiconductor layer ASI, and a source electrodeSD2 which is formed of a stacked portion constituted of the metal layerM and the semiconductor layer ASI in the same manner as the video signalline DL (drain electrode SD1) are formed.

The pixel electrode MIT is formed by etching a conductive film havinghigh optical transmissivity such as an ITO (Indium Tin Oxide) film.Further, above the pixel electrode MIT, the common electrode CT isformed by way of a second insulation layer PAS2. The pixel electrode MITis formed in a region where the pixel electrode MIT overlaps the commonelectrode CT as viewed in a plan view in a matted planar shape.

The common electrode CT is formed of a conductive film having highoptical transmissivity such as an ITO film, and is an electrode formedin a region where the common electrode CT overlaps the pixel electrodeMIT as viewed in a plan view. Plural slits SL having the longitudinaldirection thereof arranged in the extending direction of the videosignal line DL are formed in the common electrode CT. The commonelectrode CT is formed by applying etching treatment to the conductivefilm made of ITO or the like using a photolithography method. Analignment film not shown in the drawing is formed over the commonelectrode CT. The alignment film not shown in the drawing is made of apolyimide-based resin or the like, and is provided for aligning liquidcrystal molecules in the predetermined direction.

The constitution which connects the pixel electrode MIT and the sourceelectrode SD2 with each other in a conductive state is explained here.

The TFT substrate 20 includes overlapping portions 50, joining portions60 and contact holes TH.

The overlapping portion 50 is a stacked portion constituted of thesemiconductor layer ASI and the metal layer M formed on a surface of thesemiconductor layer ASI on a liquid-crystal-material-40 side, and alsois a portion which overlaps a surface of the pixel electrode MIT on aliquid-crystal-material-40 side. As shown in FIG. 3, the sourceelectrode SD2 is formed including such an overlapping portion 50.

The joining portion 60 is a portion which leads to the surface of thepixel electrode MIT on the liquid-crystal-material-40 side from asurface of the source electrode SD2 of the overlapping portion 50 on aliquid-crystal-material-40 side via an edge portion of the overlappingportion 50.

The contact hole TH is a square columnar opening portion formed in thesecond insulation layer PAS2 and is provided for exposing the joiningportion 60.

A conductive film 70 made of ITO which forms the common electrode CT isformed over the whole surface of the contact hole TH.

Accordingly, the conductive film 70 is formed on the joining portion 60exposed by the contact hole TH so that the pixel electrode MIT and thesource electrode SD2 are connected with each other in a conductivestate.

In the counter substrate 30, a light blocking film BM which is referredto as a black matrix and color filters CF are formed on a surface of aninsulation substrate SUB2 formed of a glass substrate or the like. Thelight blocking film BM is formed into a grid pattern by etching aconductive film or an insulation film having light blocking property,for example, such that the respective pixels PIX are separated from eachother.

The color filters CF are, for example, formed by applying etchingtreatment to an insulation film using a photolithography method, and areformed in opening regions of the light blocking film BM in a state wherea filter allocated to a display of R (red), a filter allocated to adisplay of G (green) and a filter allocated to a display of B (blue) arearranged periodically. An alignment film not shown in the drawing isformed over the light blocking film BM and the color filters CF by wayof an overcoat layer OC, for example.

Next, manufacturing steps of the TFT substrate 20 shown in FIG. 3 areexplained in conjunction with FIG. 4A to FIG. 8B. FIG. 4A, FIG. 5A, FIG.6A, FIG. 7A and FIG. 8A are views showing the manufacturing steps of theTFT substrate 20 shown in FIG. 3, and FIG. 4B, FIG. 5B, FIG. 6B, FIG. 7Band FIG. 8B are cross-sectional views of the structures shown in FIG.4A, FIG. 5A, FIG. 6A, FIG. 7A and FIG. 8A taken along a line 4B-4B, aline 5B-5B, a line 6B-6B, a line 7B-7B and a line 8B-8B respectively. 5sheets of photo masks are used in the manufacture of the TFT substrate20.

Firstly, the scanning signal lines GL and gate electrodes GD are formedon the surface of the insulation substrate SUB1 on theliquid-crystal-material-40 side (see FIG. 4A and FIG. 4B). To be morespecific, a metal layer made of an aluminum material or the like isformed on the surface of the insulation substrate SUB1 on theliquid-crystal-material-40 side and, thereafter, etching treatment isapplied to the metal layer using a photolithography method thus formingthe scanning signal lines GL and the gate electrodes GD.

Next, the first insulation layer PAS1 is formed, and the pixelelectrodes MIT is formed over the first insulation layer PAS1 (see FIG.5A and FIG. 5B). The pixel electrodes MIT are formed such that an ITOfilm is formed over the first insulation layer PAS1 and, thereafter,etching treatment is applied to the ITO film using a photolithographymethod.

Subsequently, the video signal lines DL, the drain electrodes SD1 andthe source electrodes SD2 are formed (see FIG. 6A and FIG. 6B). Thedrain electrode SD1 and the source electrode SD2 are formed such thatthe semiconductor layer ASI is formed over the first insulation layerPAS1 and the pixel electrode MIT, the metal layer M made of an aluminummaterial or the like is formed over the semiconductor layer ASI, andcollective etching treatment is applied to the semiconductor layer ASIand the metal layer M using a half exposure technique. Due to suchtreatment, the overlapping portion 50 which is a stacked portionconstituted of the semiconductor layer ASI and the source electrode SD2and also is a portion which overlaps an upper surface of the pixelelectrode MIT is formed.

Since etching treatment is applied to the semiconductor layer ASI andthe metal layer M collectively, the video signal lines DL, the sourceelectrode SD2 and the drain electrode SD1 are formed of the stackedportion which is constituted of the metal layer M and the semiconductorlayer ASI respectively. Accordingly, in the step of forming the videosignal lines DL, the drain electrodes SD1 and the source electrodes SD2,the semiconductor layer ASI is present between the source electrode SD2and the pixel electrode MIT and hence, the pixel electrode MIT and thesource electrode SD2 are not connected with each other in a conductivestate.

Next, the second insulation layer PAS2 and the contact holes TH areformed (see FIG. 7A and FIG. 7B). To be more specific, the secondinsulation layer PAS2 is formed between the pixel electrodes MIT and thecommon electrodes CT, that is, the second insulation layer PAS2 isformed over the video signal lines DL, the drain electrodes SD1, thesource electrode SD2 and the pixel electrodes MIT, while the contactholes TH are formed by etching treatment using a photolithographymethod. The joining portion 60 is exposed by the contact hole TH.

The contact holes TH are formed in the second insulation layer PAS2which is an insulation layer arranged close to a surface of the TFTsubstrate 20 on a liquid-crystal-material-40 side and hence, the contactholes TH can be formed along with the contact holes formed in terminalsused for connection with the data drive circuit 11 and the scanningdrive circuit 12 (not shown in the drawing). That is, it is unnecessaryto provide a step exclusively provided for forming the contact holes TH.

Next, the common electrodes CT are formed over the second insulationlayer PAS2 (see FIG. 8A and FIG. 8B). In forming the common electrodesCT, a conductive film 70 made of ITO is formed over the secondinsulation layer PAS2, and etching treatment using a photolithographymethod is applied to the conductive film 70 thus forming the commonelectrodes CT each having slits SL. Further, the conductive film 70 isformed over the whole surface of the contact hole TH and hence, thejoining portion 60 which is exposed by the contact hole TH is covered bythe conductive film 70. Due to such treatment, the pixel electrode MITand the source electrode SD2 are connected with each other in aconductive state.

In the liquid crystal display device 1 and the manufacturing methodthereof according to the embodiment of the present invention, the sourceelectrodes SD2 each of which includes the overlapping portion 50 whichis the stacked portion constituted of the semiconductor layer ASI andthe metal layer M formed over the surface of the semiconductor layer ASIon the liquid-crystal-material-40 side and is a portion which overlapsthe surface of the pixel electrode MIT on the liquid-crystal-material-40side, the video signal lines DL each of which is formed of the stackedportion constituted of the metal layer M and the semiconductor layerASI, and the drain electrodes SD1 each of which is formed of the stackedportion constituted of the metal layer M and the semiconductor layer ASIare formed, the contact holes TH each of which exposes the joiningportion 60 which is the portion leading to the surface of the pixelelectrode MIT on the liquid-crystal-material-40 side from the surface ofthe source electrode SD2 on the liquid-crystal-material-40 side via theedge portion of the overlapping portion 50 are formed in the secondinsulation layer PAS2, and the conductive film 70 which is formed intothe common electrode CT is formed over the joining portion 60 exposed bythe contact hole TH.

In this manner, after forming the pixel electrode MIT, the video signallines DL, the semiconductor layer ASI, the drain electrodes SD1 and thesource electrode SD2 can be formed by collective etching treatment.Accordingly, a disconnection defect of the video signal lines DL can bereduced, and the number of photo masks to be used can be suppressed to 5sheets.

Further, the semiconductor layers ASI are formed after forming thescanning signal lines GL and hence, the accuracy in mask alignment canbe easily acquired compared to a case where the scanning signal lines GLare formed after forming the semiconductor layers ASI.

Accordingly, a yield can be enhanced while reducing a manufacturingcost, and a process design can be easily provided.

Further, in the liquid crystal display device 1 and the manufacturingmethod thereof according to the embodiment of the present invention, thecontact holes TH are formed in the second insulation layer PAS2 which isan insulation layer close to the surface of the TFT substrate 20 on theliquid-crystal-material-40 side and hence, the contact holes TH can beformed along with the formation of other contact holes formed in theterminals on the TFT substrate 20. That is, it is unnecessary to providea step for forming the contact holes TH thus easily providing a processdesign eventually.

In the liquid crystal display device 1 and the manufacturing methodthereof according to the embodiment of the present invention, theconductive film 70 formed on the common electrode CT is formed on thejoining portion 60 exposed by the contact hole TH and hence, at the timeof forming the common electrode CT, the source electrode SD2 and thepixel electrode MIT can be connected with each other in a conductivestate. That is, it is unnecessary to provide a step for connecting thesource electrode SD2 and the pixel electrode MIT in a conductive statewhereby it is possible to easily provide a process design eventually.

[Modification]

Next, a liquid crystal display device 1 according to a modification ofthe embodiment of the present invention is explained in conjunction withFIG. 9. FIG. 9 is a view showing the liquid crystal display device 1according to the modification of the embodiment of the presentinvention. In the liquid crystal display device 1 according to theembodiment of the present invention, exemplified is the constitutionwhere the overlapping portion 50 overlaps the pixel electrode MIT in theextending direction of the video signal lines DL and the contact hole THis formed at the position where the joining portion 60 formed by theoverlapping portion 50 is exposed. In the liquid crystal display device1 according to the modification, as shown in the drawing, an overlappingportion 51 overlaps the pixel electrode MIT in the direction orthogonalto the extending direction of the video signal line DL, and the contacthole TH is formed at a position where an upper portion of a joiningportion 61 formed by the overlapping portion 51 is opened. Thismodification can also acquire the substantially same advantageouseffects as the embodiment.

In the embodiment of the present invention, the constitution where theslits SL having the longitudinal direction thereof arranged in theextending direction of the video signal line DL are formed in the commonelectrode CT is exemplified. However, a shape of the slits SL is notlimited to such a shape. For example, slits SL arranged in the directionwhich obliquely intersects the extending direction of the video signallines DL may be formed in the common electrode CT.

Further, in the embodiment of the present invention, the constitutionwhere the whole surface of the contact hole TH which constitutes theopening portion is covered with the conductive film 70 is exemplified.However, the present invention is not limited to such a constitution.That is, it is sufficient that at least the joining portion 60 iscovered with the conductive film 70.

Although the square columnar contact hole TH is exemplified as theopening portion in the embodiment of the present invention, the presentinvention is not limited to such an opening portion. For example, acircular columnar contact hole may be used as the opening portion.

While there have been described what are at present considered to becertain embodiments of the invention, it will be understood that variousmodifications may be made thereto, and it is intended that the appendedclaims cover all such modifications as fall within the true spirit andscope of the invention.

What is claimed is:
 1. A liquid crystal display device comprising: afirst insulation substrate and a second insulation substrate which holda liquid crystal material therebetween; a pixel electrode; a commonelectrode; and a thin film transistor which has a semiconductor layer, afirst electrode connected with a video signal line, and a secondelectrode connected with the pixel electrode; wherein the semiconductorlayer overlaps and is in physical contact with the pixel electrode; andwherein a part of the pixel electrode, a part of the semiconductorlayer, and a part of the second electrode are stacked at an overlappingportion.
 2. The liquid crystal display device according to claim 1,wherein an insulation layer is formed on the pixel electrode; andwherein the insulation layer has an opening which exposes theoverlapping portion.
 3. The liquid crystal display device according toclaim 2, wherein a conductive film is formed over the overlappingportion; and wherein the conductive film is on and in physical contactwith the pixel electrode at a first portion, and with the secondelectrode at a second portion which is different from the first portion.4. The liquid crystal display device according to claim 3, wherein theconductive film covers the whole surface of the opening of theinsulation layer.
 5. The liquid crystal display device according toclaim 3, wherein the conductive film is in physical contact with an edgeportion of the semiconductor layer and with an edge portion of thesecond electrode.
 6. The liquid crystal display device according toclaim 3, wherein the insulation layer is formed between the pixelelectrode and the common electrode; and wherein the conductive film andthe common electrode are formed at a same layer.